1. Field of the Invention
This invention relates to the field of automotive transmissions in which speed ratio changes are produced automatically. It pertains particularly to the kinematic arrangement and its actuation system for controlling such transmissions.
2. Description of the Prior Art
Conventional automatic transmissions for automotive use employ planetary gearsets, certain components of which are continually mutually interconnected, components that are selectively connected to other components through operation of clutches, and components that are selectively held against rotation by brakes. The selective, alternate application and release of the clutches and brakes produce the desired forward and reverse speed ratios. Gearing for such transmissions generally is epicyclic gearing, i.e., a system of gears in which one or more gears travel around the inside or outside of another gear whose axis is fixed. An epicyclic train is a combination of epicyclic gears, in which some or all the gears rotate about an axis and translate or revolve around that axis.
U.S. Pat. No. 787,908 describes a manual transmission producing a direct drive forward speed ratio and forward and reverse low speed ratios by alternately engaging two brake bands and a clamping disc, each associated with one of these speed ratios. The transmission includes a cluster pinion having three gears, each pinion meshing with a gear driven by an engine shaft.
U.S. Pat. No. 1,005,186 describes a transmission that produces low speed forward drive and reverse drive by selective engaging brake bands for holding sun gears against rotation. A cluster gear having three planet pinions meshes with an output sun gear, a forward drive sun gear and a reverse drive sun gear, respectively. A friction clutch driveably connects the transmission output and a drive shaft.
Each of these transmissions produces reverse drive and low speed forward drive by alternately depressing pedals that cause engagement of a corresponding brake band. Direct drive results when these pedals are released. The axial position of each brake band is fixed so that the band continually surrounds the corresponding brake drum; its position is not altered by any other action including manipulation of a gear selector lever by the vehicle operator.